1. Field of the Invention
This invention relates in general to storage devices and more particularly to the detection of the pressure in hard disk drives.
2. Description of Related Art
Hard disk drives are magnetic storage devices that contain at least one rotatable magnetic disk, a magnetic recording head for reading data and/or writing data, a slider for supporting the magnetic recording head in proximity to the disk, a suspension assembly for resiliently supporting and biasing the slider against the disk, and a positioning actuator coupled to the recording head/slider/suspension assembly for moving the recording head over the surface of the disk. In some of the conventional magnetic disk drives, the slider rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The bearing of air is affected by the atmospheric pressure within the hard disk drive and can vary depending on the operating environment conditions. For example, the development of the laptop has resulted in the use of computers in higher and lower pressure locations. Hard disk drives may be placed in service where they are subjected to pressure, temperature, and humidity changes. At low pressure the lift capacity of the slider is reduced, which reduces the air bearing height between the head and disk. This action increases the chances of a hard drive head crash, which is a catastrophical event for the disk drive because it renders it useless.
Prior attempts were made to compensate for changes in the operating atmospheric pressure. Typically, separate sensors have been used to detect changes in different parameters arising from environmental changes to the hard disk drive. U.S. Pat. No. 6,011,666 disclosed the use of different sensors to detect different environmental parameters. The detected information is used for adjusting the rotational speed of the disk and/or controlling the head to carry out seek operations. Assignee""s Patent No. 6,067,203 disclosed a method that involved using a dedicated pressure sensor for detecting the operating atmospheric pressure in a hard disk drive to control the rotational velocity of the disk to one of the appropriate discrete disk velocities when the atmospheric pressure reaches a predefined threshold.
There are several disadvantages associated with using a dedicated atmospheric pressure sensor in a hard disk drive practiced in prior art. The dedicated pressure sensor adds to the component cost, requires internal space for mounting, increases risk of component failure, and adds additional electronic circuitry. What is needed is a disk drive with a pressure sensoring capability that does not have any of the disadvantages of prior art disk drives that use a conventional pressure sensor.
The present invention overcomes the drawbacks of the prior art by applying the changes in thermal characteristics of a magnetic head to determine the operating pressure in an enclosed storage unit. In one particular embodiment, the present invention measures the internal pressure of a hard disk drive, based on the thermoresistive characteristic of a magnetoresisitive (MR) head. A relationship exists between the MR head temperature, internal pressure, and internal operating temperature, with the pressure inversely dependent on head temperature at a given operating temperature.